I lost all my FireFox bookmarks due to not being careful. I got my Chrome ones, but the FF were the most important. One can continue to live despite losing all bookmarks!
did you uninstall FF ? generally, it doesn’t remove user data...so your bookmarks might still be there.
If you want to try, PM me and we might be able to salvage them ?
for next time. easy way to create a backup of your bookmarks is: to create an “export” file.
Launch Brave and open the Main menu: newmenuicon.png
Select Bookmarks > Bookmarks Manager
Open the More options menu at the top right
Select Export and choose where you want to store the exported file.